Slurry explosives compositions have achieved wide acceptance as commercial explosives owing to their relative low cost, safety and inherent water-resistance. These explosives generally contain a continuous liquid phase comprising an inorganic oxidizer salt solution, a thickening agent for the liquid phase, water and/or water-miscible liquid organics, particulate fuel and/or sensitizer, and, optionally, trace ingredients such as gassing and cross-linking agents. These compositions can have varying rheology and generally can be pumped as fluids at least initially after formulation. They can be used successfully in water-containing boreholes due to their water-resistance.
A specialized use of slurry explosive compositions is in the permissible explosive field. Generally, permissible explosives are those which are cap-sensitive and relatively nonincendive so that they can be used in underground mines having potentially flammable atmospheres, such as underground coal mines. The United States Department of Labor Mine, Safety and Health Administration has established detailed requirements for approval of permissible explosives for underground use. These requirements are published in 30 C.F.R. Part 15. These regulations, which are incorporated herein by reference, define permissible explosives in terms of minimum requirements, which are somewhat stringent. Co-pending application Ser. No. 186,371 discloses a permissible slurry explosive comprising inorganic nitrate oxidizer salts, water, inert material such as sodium chloride, finely flaked aluminum particles and cross-linking and thickening agents. The present invention discloses a permissible explosive composition containing relatively high amounts of sodium perchlorate, which ingredient has been prohibited for use in permissible compositions in the United States and certain other countries. The compositions also contain high amounts of a polysaccharide polymer of plant origin, preferably a starch. This ingredient acts as a thickener and fuel in the composition.
With compositions of the present invention, it is particularly important to prevent leakage or leaching of the sodium perchlorate solution, which becomes highly flammable if allowed to dry in the presence of a fuel such as packaging material. The use of high amounts of polysaccharide polymer is necessary to provide sufficient thickening to prevent leakage or leaching. Others have employed starches or fibrous or pulpy plant matter as thickeners in explosive compositions containing solutions of inorganic oxidizer salts. For example, U.S. Pat. No. 3,507,718 discloses an explosive slurry containing pulpy fibrous matter; however, additional thickeners such as starch or gum generally are required since the cellular materials described in this patent are essentially insoluble on non-hydratable in water, in contrast to the more soluble or hydratable finely divided polysaccharide polymer employed in the present invention. U.S. Pat. No. 3,361,604 discloses an explosive slurry containing plant matter as a combined thickening agent and fuel. The disclosed fibrous pulpy plant matter is similar to that disclosed in U.S. Pat. No. 3,507,718 described above, and thus differs from the polysaccharide polymer of the present invention. Small amounts of polysaccharide polymers have been used in explosive compositions as thickeners. See, for example, U.S. Pat. Nos. 3,713,917; 3,350,246; 3,378,415; and 3,522,117. The present invention, however, requires considerably more polysaccharide polymer. In addition, the present invention requires the specific combination of high amounts of polysaccharide polymer with a sodium perchlorate solution, and none of the prior art references disclose this combination. Although some of the prior art references referred to above suggest that sodium perchlorate may be used as a supplemental oxidizer salt, ammonium nitrate is the principal salt used.
The combination of sodium perchlorate and polysaccharide polymer in the present invention offers several advantages over compositions of the prior art. These advantages include:
1. The use of a high concentration of polysaccharide polymer as a thickener and fuel prevents leaking or leaching of the sodium perchlorate solution from the composition. This minimizes the hazard of using sodium perchlorate. In addition, the use of the polysaccharide polymer as thickener imparts to the composition a tough, rubbery rheology, which minimizes the degree of contact of the composition with foreign materials in the event of spills or accidents. Thus, the flammability hazard is further reduced.
2. The polysaccharide polymers will hydrate in the sodium perchlorate solution at ambient temperature, which is a safe temperature for manufacturing. Many prior art compositions require elevated and thus more hazardous manufacturing temperatures.
3. The compositions retain their sensitivity over a relatively wide density range. The compositions also are relatively temperature insensitive from -20.degree. C. to 30.degree. C. Thus the compositions can be used under many different blasting conditions covering wide extremes of climate or bulk energy needs.
4. The compositions do not require the use of expensive thickening agents such as gums.
5. The compositions for excellent permissible explosives. Upon reaction the sodium perchlorate forms sodium chloride, which acts as a flame retardant for the detonation products. In fact, sodium chloride commonly is added to a permissible explosive for purposes of flame retardation. The in situ formation of sodium chloride from sodium perchlorate is preferable, however, to the separate addition of sodium chloride, since sodium chloride is an inert which reduces the energy of the composition, whereas sodium perchlorate is a reactant. Moreover, the concentration of sodium perchlorate in the compositions of the present invention is preferably about 50%, which produces about 24% sodium chloride in the products of detonation. To add this amount of sodium chloride as an inert would considerably reduce the energy and sensitivity of the composition. The compositions also contain a high water content and require less aluminum for sensitization than do nitrate oxidized slurries. The lower aluminum level and the higher water level further lower incendivity. Finally, the high amount of polysaccharide polymer thickener restricts crystal growth of solid crystals of sodium perchlorate further minimizing incendivity at low temperatures where salts could precipitate from solution. Accordingly, the compositions are excellent for permissible use, even though sodium perchlorate heretofore has been considered too hazardous for permissible use and in fact has been prohibited in certain countries.